ABSTRACT The objective of the proposed research is to apply ultrasound image-guided high intensity focused ultrasound (HIFU)-based technique termed histotripsy to liquefy large soft tissue hematomas for subsequent fine needle aspiration and to demonstrate the safety, feasibility, and efficiency of this intervention. Large intra-abdominal, retroperitoneal, and intramuscular hematomas are common consequences of sharp and blunt trauma and postsurgical bleeds, and often threaten organ failure, compartment syndrome or spontaneous infection. Current therapy options include surgical evacuation and installation of indwelling drains that are not effective due to the viscosity of the organized hematoma. Histotripsy techniques have been previously successfully applied to and optimized for the liquefaction of intravascular thrombi, but not for the large traumatic hematomas that are much larger in volume and require substantially faster liquefaction rates to complete the treatment within clinically relevant time frame (15-20 minutes). To achieve our objective, we propose to identify the histotripsy treatment protocols that yield maximum thrombolysis rates for specific hematoma shapes and anatomic locations. SA1 will address treatment efficiency and include in vitro investigation of the influence of specific modifications to HIFU transducer design (focusing angle and operating frequency) and treatment protocols (pulse duration, exposure duration, spatial scanning strategies) on the hematoma liquefaction rate. Clotted bovine blood with varying concentrations of thrombin embedded into gel molds, with shapes replicating the CT images of traumatic hematoma cases, will be liquefied, and the total liquefied volume divided by treatment time will serve as the outcome measure. SA2 will address treatment feasibility by evaluating the influence of intervening tissue aberrations, attenuation, and obstacles (e.g. ribs) on treatment planning and treatment parameters (spatial scanning strategies, required power). Studies will be performed in hematoma samples placed behind porcine body wall and ribs, using a preclinical histotripsy system that will be designed and fabricated based on the results from SA1. SA3 will include in vivo evaluation of the treatment safety and feasibility in acute studies in swine. Large hematomas will be created by bleeding from puncture injuries to peripheral vessels in the relevant anatomic locations (spleen, retroperitoneum, and femoral artery) by intravascular catheters. The hematomas will be liquefied using the treatment methodology developed in SA1 and 2, and the lysate immediately aspirated with a small needle under ultrasound image guidance. Treatment safety in terms of potential mechanical damage to the intervening tissues and organs will be evaluated histologically. We expect that these studies will initiate the clinical translation of this technology and lead directly to the application for an Investigational Device Exemption to US FDA and the design of the first clinical trial. The proposed approach would provide a way for safer and more efficient way to clinically manage large hematomas.